1. Field of the Invention
The present invention relates to a borescope apparatus capable of jetting a compressed fluid from a jet port in an insertion section so that the insertion section is moved by the impellent force of the fluid jet.
2. Description of the Related Art
A typical industrial borescope apparatus is disclosed in U.S. Pat. No. 4,753,501, for example. In this borescope, a jet port is formed sidelong at the distal end portion of a flexible insertion section. A compressed fluid, such as high-pressure air, is jetted from the jet port so that the insertion section is subjected to reaction from the impellent force of the fluid jet. Thus, the insertion section can be moved opposite to the jet direction of the compressed fluid.
Many of the borescopes of this type are widely used for industrial applications. For example, they are used for the inspection of the interior of gas pipes, tanks, or wing cavities of large-sized airplanes. Since the insertion section of these borescopes can be raised, all the corners of even a vertically extending cavity can be observed through the insertion section.
According to these conventional borescopes, however, the insertion section is raised with the force of gravity and a thrust from a fluid jet delicately balanced, as its distal end portion is brought close to an objective region of inspection to facilitate the observation. In general, therefore, the raised posture of the insertion section is unstable. Consequently, the distal end of the insertion section is liable to a fine deflection during the observation, so that a stable image cannot be observed for a close inspection.